1. Field of the Invention
This invention relates in general to water filtering systems and more particularly to a filtering system for use in filtering water supplies having a high rate of contamination, such as the water supply used in water cooled air conditioning systems.
2. Description of the Prior Art
With the significant increases in energy costs in the last several years, it has become essential that ways be found to reduce energy consumption and to reduce whatever other costs are associated with equipment operation in general and cooling systems in particular. As a result, significant improvements have been made in building insulation, air leakage and the like.
However, the primary focus for reducing operating costs in cooling systems must be related to the cooling systems themselves. Even if it is only possible to reduce operating costs by a small percentage, significant savings can be realized over a period of time.
Many air conditioning, or refrigeration, systems include what may be considered as a closed loop cooling system wherein a refrigerant is recirulatingly moved from a chiller to a load. When the refrigerant passes through the load, it picks up heat and carries it back to the chiller. The chiller includes a compressor and a condenser with the function of the condenser being to extract the heat from the refrigerant and dissipate that extracted heat. In most residential and other relatively small cooling systems, heat is extracted from the condenser by moving air across the condenser. However, in most commercial or industrial cooling system installations water is used to cool the consenser.
In the relatively large cooling systems such as the commercial or industrial installations mentioned above, the condenser is located in a cooling tower and water is recirculated through the tower in an open loop between spray nozzles located in the top of the cooling tower and a water collection sump located in the bottom of the tower. Thus, the condenser is cooled by evaporation of the water as it is sprayed down through the condenser.
As is well known, whenever evaporation takes place, the mineral concentration in the remaining water will increase and precipitation of the salt compounds results. The precipitated salts collect on the heat exchange surfaces of the condenser and form an insulative coating thereon which reduces the heat transfer capacity. In that a cooling tower is an open loop system, airborne contaminants also collect in the water such as dust, dirt, bacteria and the like. All of these contaminants cause fouling of the condenser and the cooling tower and can rapidly decrease the efficiency thereof. Due to cooling tower and condenser fouling, most cooling systems employ two cooling towers so that one can be used while the other is being cleaned. For example, in a rather dusty and arid area a typical cooling tower may need to be shut down for cleaning as often as once a week. This is, of course, very expensive from a labor standpoint and adds to the total operating costs of the cooling system.
In an attempt to help alleviate the condenser and cooling tower fouling problem, many cooling towers are provided with a bleed-off system which continuously extracts some of the contaminated water from the cooling tower and directs that waste water to a suitable disposal point. There are two problems with bleed-off systems. First, a bleed-off system, while being better than nothing, is not a very effective way of controlling fouling. And, secondly, a bleed-off system wastes a considerable amount of water and the water conditioning chemicals that are addedd thereto and adds significantly to the amount of make-up water that must be supplied to the cooling tower.
In many regions, water conservation is extremely important and cooling towers with bleed-off systems are falling into disfavor due to the large quantities of water and chemicals that are wasted by towers that are so equipped. In addition to the water and chemical conservation considerations, the costs of water must also be added to the total operating expense of the cooling systems.
In addition to the fouling of condensers and cooling towers, a build-up of solid particles in water circulation pipes will increase pipe friction and dynamic head losses, and the circulation of abrasive solids will increase wear on seals, pump parts and other system components.
In some instances, water filtration systems are employed and filtration will help reduce all of the undesirable factors that are inherent in cooling towers and other water bodies particularly those having a high rate of contamination.
The most common water filtering systems currently being used in some cooling towers are of the sand media filtration type. While such sand filters are a considerable improvement over the above described bleed-off systems, they have two shortcommings. First, sand filters are limited to their filtration effectiveness and are unable to remove suspended solids which are smaller than about 40-50 microns. Thus, many suspended solids which should ideally be removed from cooling tower water cannot be removed by a sand filter. Secondly, sand filters when used in cooling tower installations must be backwashed quite often and they waste considerable quantities of water and chemicals during a backwash cycle.
Therefore, a need exists for a new and improved water filtering system which overcomes some of the problems and shortcommings of the prior art.